Methods and systems for humidity and pcv flow detection via an exhaust gas sensor

ABSTRACT

Methods and systems are provided for estimating a PCV flow to an engine based on the output of an exhaust gas oxygen sensor. During DFSO conditions, a reference voltage of the sensor is modulated initially with an intake throttle open and then with the intake throttle closed. PCV flow leaking past the piston valves in an aging engine, as well as an ambient humidity estimate, are inferred based on the outputs of the sensor during the modulating with the intake throttle open and closed.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 13/745,639, filed on Jan. 18, 2013, the entirecontents of which are hereby incorporated by reference for all purposes.

TECHNICAL FIELD

The present application relates generally to ambient humidity detectionvia an exhaust gas sensor coupled in an exhaust system of an internalcombustion engine.

BACKGROUND AND SUMMARY

During engine non-fueling conditions in which at least one intake valveand one exhaust valve are operating, such as deceleration fuel shut off(DFSO), ambient air may flow through engine cylinders and into theexhaust system. In some examples, an exhaust gas sensor may be utilizedto determine ambient humidity during the engine non-fueling conditions.However, due to intake throttle closure during the engine non-fuelingcondition, a large intake manifold vacuum is generated which can draw inpositive crankcase ventilation (PCV) hydrocarbons. As such, even if aPCV port is closed during the DFSO, the vacuum may be sufficientlystrong to draw in PCV hydrocarbons through the piston rings. The PCVflow drawn in may be aggravated in an aging engine due to leakage of PCVgases past the piston rings and valves. The ingested hydrocarbons affectthe output of the exhaust gas sensor and can confound the humiditymeasurements. In particular, the hydrocarbon effect leads to a sensoroutput that overestimates the ambient humidity.

The inventors herein have recognized the above issue and have devised anapproach to at least partially address it. Thus, a method for an enginesystem which includes an exhaust gas sensor is disclosed. In oneexample, the method includes, during engine non-fueling conditions,where at least one intake valve and one exhaust valve are operating,modulating a reference voltage of an exhaust gas sensor with an intakethrottle closed and open; and indicating engine degradation based on PCVflow, the positive crankcase ventilation (PCV) flow based on outputs ofthe sensor during the modulating. The method may further comprisegenerating an indication of ambient humidity based on an output of theexhaust gas sensor with the intake throttle closed and the estimated PCVflow. In this way, a more accurate ambient humidity estimate may beachieved and PCV flow may be better estimated and accounted for.

For example, during selected deceleration fuel shut off (DFSO) events,an engine controller may modulate the reference voltage of an intakeoxygen sensor to estimate each of an ambient humidity and a PCV flow.The controller may first modulate the reference voltage with the intakethrottle open and then re-modulate the voltage with the intake throttleclosed. With the intake throttle open, manifold pressure is increasedand PCV flow to the intake is reduced. During such conditions, a changein pumping current read at the sensor during the modulating isindicative of an ambient humidity. With the intake throttle closed,manifold pressure is decreased and PCV flow to the intake is increased.During such conditions, a change in pumping current read at the sensorduring the modulating is indicative of an ambient humidity as well as aneffect of PCV hydrocarbons. By comparing the change in pumping currentsestimated with the intake throttle open and closed, an amount of PCVflow received in the engine during closed throttle conditions can beidentified. If the PCV port was also closed during the modulating, thePCV flow can be compared to a threshold to identify PCV flow leakagepast piston rings and an indication of engine aging and componentdegradation can be signaled. The ambient humidity can also be furthermodified based on the learned PCV flow. The more reliable ambienthumidity estimate, free of hydrocarbon effects from PCV, can then beused to adjust engine operating parameters without incurring enginecontrol issues.

In this way, the PCV impact on humidity measurement by an exhaust gasoxygen sensor is reduced. By selectively opening the intake throttleduring a DFSO when humidity measurement is required, intake manifoldvacuum is reduced, lowering the amount of PCV hydrocarbons drawn intothe engine. In addition, even if any PCV hydrocarbons are ingested, theincreased airflow reduces the PCV concentration sensed by the exhaustgas sensor during the DFSO. As such, the ambient humidity may bedetermined more accurately and reliably.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example embodiment of a combustion chamber in an enginesystem including an exhaust system and an exhaust gas recirculationsystem.

FIG. 2 shows a schematic diagram of an example exhaust gas sensor.

FIG. 3 is a flow chart illustrating a routine for determining ameasurement mode of an exhaust gas sensor.

FIG. 4 is a flow chart illustrating a routine for determining ambienthumidity based on an exhaust gas sensor.

FIG. 5 shows a graph illustrating effect of PCV hydrocarbons on humidityestimation.

FIG. 6 is a flow chart illustrating a routine for adjusting engineoperating parameters based on an ambient humidity generated by anexhaust gas sensor.

FIG. 7 shows an example impact of PCV flow on humidity determination.

DETAILED DESCRIPTION

The following description relates to methods and systems for an enginesystem with an exhaust gas oxygen sensor, such as the engine system ofFIG. 1 and the exhaust gas oxygen sensor of FIG. 2. During selectedengine non-fueling conditions, the exhaust gas oxygen sensor may be usedfor humidity estimation and/or PCV flow estimation. A controller of theengine system may be configured with code to perform a control routine,such as the routines of FIGS. 3-4 to modulate a reference voltageapplied to the exhaust gas oxygen sensor during the engine non-fuelingconditions with an intake throttle open, and then again with the intakethrottle closed. By comparing the outputs of the sensor during themodulating, the controller may learn the ambient humidity as well as aPCV flow rate. The learning may be based on the linear relationshipbetween exhaust water content and a pumping current output by the sensor(FIG. 6). The controller may then adjust one or more engine operatingparameters based on the learned humidity and PCV flow (FIG. 5).Furthermore, the controller may also identify engine componentdegradation leading to PCV leakage based on the learned PCV flow. Anexample adjustment is shown with reference to FIG. 7.

FIG. 1 is a schematic diagram showing one cylinder of a multi-cylinderengine 10 in an engine system 100, which may be included in a propulsionsystem of an automobile. The engine 10 may be controlled at leastpartially by a control system including a controller 12 and by inputfrom a vehicle operator 132 via an input device 130. In this example,the input device 130 includes an accelerator pedal and a pedal positionsensor 134 for generating a proportional pedal position signal PP. Acombustion chamber (i.e., cylinder) 30 of the engine 10 may includecombustion chamber walls 32 with a piston 36 positioned therein. Thepiston 36 may be coupled to a crankshaft 40 so that reciprocating motionof the piston is translated into rotational motion of the crankshaft.The crankshaft 40 may be coupled to at least one drive wheel of avehicle via an intermediate transmission system. Further, a startermotor may be coupled to the crankshaft 40 via a flywheel to enable astarting operation of the engine 10.

The combustion chamber 30 may receive intake air from an intake manifold44 via an intake passage 42 and may exhaust combustion gases via anexhaust passage 48. The intake manifold 44 and the exhaust passage 48can selectively communicate with the combustion chamber 30 viarespective intake valve 52 and exhaust valve 54. In some embodiments,the combustion chamber 30 may include two or more intake valves and/ortwo or more exhaust valves.

In this example, the intake valve 52 and exhaust valve 54 may becontrolled by cam actuation via respective cam actuation systems 51 and53. The cam actuation systems 51 and 53 may each include one or morecams and may utilize one or more of cam profile switching (CPS),variable cam timing (VCT), variable valve timing (VVT), and/or variablevalve lift (VVL) systems that may be operated by the controller 12 tovary valve operation. The position of the intake valve 52 and exhaustvalve 54 may be determined by position sensors 55 and 57, respectively.In alternative embodiments, the intake valve 52 and/or exhaust valve 54may be controlled by electric valve actuation. For example, the cylinder30 may alternatively include an intake valve controlled via electricvalve actuation and an exhaust valve controlled via cam actuationincluding CPS and/or VCT systems.

A fuel injector 66 is shown coupled directly to combustion chamber 30for injecting fuel directly therein in proportion to the pulse width ofsignal FPW received from the controller 12 via an electronic driver 68.In this manner, the fuel injector 66 provides what is known as directinjection of fuel into the combustion chamber 30. The fuel injector maybe mounted in the side of the combustion chamber or in the top of thecombustion chamber (as shown), for example. Fuel may be delivered to thefuel injector 66 by a fuel system (not shown) including a fuel tank, afuel pump, and a fuel rail. In some embodiments, the combustion chamber30 may alternatively or additionally include a fuel injector arranged inthe intake manifold 44 in a configuration that provides what is known asport injection of fuel into the intake port upstream of the combustionchamber 30.

The intake passage 42 may include a throttle 62 having a throttle plate64. In this particular example, the position of throttle plate 64 may bevaried by the controller 12 via a signal provided to an electric motoror actuator included with the throttle 62, a configuration that iscommonly referred to as electronic throttle control (ETC). In thismanner, the throttle 62 may be operated to vary the intake air providedto the combustion chamber 30 among other engine cylinders. The positionof the throttle plate 64 may be provided to the controller 12 by athrottle position signal TP. The intake passage 42 may include a massair flow sensor 120 and a manifold air pressure sensor 122 for providingrespective signals MAF and MAP to the controller 12.

An exhaust gas sensor 126 is shown coupled to the exhaust passage 48upstream of an emission control device 70. The sensor 126 may be anysuitable sensor for providing an indication of exhaust gas air/fuelratio such as a linear oxygen sensor or UEGO (universal or wide-rangeexhaust gas oxygen), a two-state oxygen sensor or EGO, a HEGO (heatedEGO), a NO_(x), HC, or CO sensor. The emission control device 70 isshown arranged along the exhaust passage 48 downstream of the exhaustgas sensor 126. The device 70 may be a three way catalyst (TWC), NO_(x)trap, various other emission control devices, or combinations thereof.In some embodiments, during operation of the engine 10, the emissioncontrol device 70 may be periodically reset by operating at least onecylinder of the engine within a particular air/fuel ratio.

Further, in the disclosed embodiments, an exhaust gas recirculation(EGR) system 140 may route a desired portion of exhaust gas from theexhaust passage 48 to the intake manifold 44 via an EGR passage 142. Theamount of EGR provided to the intake manifold 44 may be varied by thecontroller 12 via an EGR valve 144. Further, an EGR sensor 146 may bearranged within the EGR passage 142 and may provide an indication of oneor more of pressure, temperature, and constituent concentration of theexhaust gas. Under some conditions, the EGR system 140 may be used toregulate the temperature of the air and fuel mixture within thecombustion chamber, thus providing a method of controlling the timing ofignition during some combustion modes. Further, during some conditions,a portion of combustion gases may be retained or trapped in thecombustion chamber by controlling exhaust valve timing, such as bycontrolling a variable valve timing mechanism.

The controller 12 is shown in FIG. 1 as a microcomputer, including amicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 106 in this particular example, random access memory 108,keep alive memory 110, and a data bus. The controller 12 may receivevarious signals from sensors coupled to the engine 10, in addition tothose signals previously discussed, including measurement of inductedmass air flow (MAF) from the mass air flow sensor 120; engine coolanttemperature (ECT) from a temperature sensor 112 coupled to a coolingsleeve 114; a profile ignition pickup signal (PIP) from a Hall effectsensor 118 (or other type) coupled to crankshaft 40; throttle position(TP) from a throttle position sensor; and absolute manifold pressuresignal, MAP, from the sensor 122. Engine speed signal, RPM, may begenerated by the controller 12 from signal PIP. Manifold pressure signalMAP from a manifold pressure sensor may be used to provide an indicationof vacuum, or pressure, in the intake manifold. Note that variouscombinations of the above sensors may be used, such as a MAF sensorwithout a MAP sensor, or vice versa. During stoichiometric operation,the MAP sensor can give an indication of engine torque. Further, thissensor, along with the detected engine speed, can provide an estimate ofcharge (including air) inducted into the cylinder. In one example, thesensor 118, which is also used as an engine speed sensor, may produce apredetermined number of equally spaced pulses every revolution of thecrankshaft.

The storage medium read-only memory 106 can be programmed with computerreadable data representing non-transitory instructions executable by theprocessor 102 for performing the methods described below as well asother variants that are anticipated but not specifically listed.

As described above, FIG. 1 shows only one cylinder of a multi-cylinderengine, and each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector, spark plug, etc.

FIG. 2 shows a schematic view of an example embodiment of an exhaust gassensor, such as a UEGO sensor 200 configured to measure a concentrationof oxygen (O₂) in an exhaust gas stream. The sensor 200 may operate asthe exhaust gas sensor 126 described above with reference to FIG. 1, forexample. The sensor 200 comprises a plurality of layers of one or moreceramic materials arranged in a stacked configuration. In the embodimentof FIG. 2, five ceramic layers are depicted as layers 201, 202, 203,204, and 205. These layers include one or more layers of a solidelectrolyte capable of conducting ionic oxygen. Examples of suitablesolid electrolytes include, but are not limited to, zirconiumoxide-based materials. Further, in some embodiments such as that shownin FIG. 2, a heater 207 may be disposed in thermal communication withthe layers to increase the ionic conductivity of the layers. While thedepicted UEGO sensor 200 is formed from five ceramic layers, it will beappreciated that the UEGO sensor may include other suitable numbers ofceramic layers.

The layer 202 includes a material or materials creating a diffusion path210. The diffusion path 210 is configured to introduce exhaust gasesinto a first internal cavity 222 via diffusion. The diffusion path 210may be configured to allow one or more components of exhaust gases,including but not limited to a desired analyte (e.g., O₂), to diffuseinto the internal cavity 222 at a more limiting rate than the analytecan be pumped in or out by pumping electrodes pair 212 and 214. In thismanner, a stoichiometric level of O₂ may be obtained in the firstinternal cavity 222.

The sensor 200 further includes a second internal cavity 224 within thelayer 204 separated from the first internal cavity 222 by the layer 203.The second internal cavity 224 is configured to maintain a constantoxygen partial pressure equivalent to a stoichiometric condition, e.g.,an oxygen level present in the second internal cavity 224 is equal tothat which the exhaust gas would have if the air-fuel ratio wasstoichiometric. The oxygen concentration in the second internal cavity224 is held constant by pumping current I_(cp). Herein, the secondinternal cavity 224 may be referred to as a reference cell.

A pair of sensing electrodes 216 and 218 is disposed in communicationwith first internal cavity 222 and the reference cell 224. The sensingelectrodes pair 216 and 218 detects a concentration gradient that maydevelop between the first internal cavity 222 and the reference cell 224due to an oxygen concentration in the exhaust gas that is higher than orlower than the stoichiometric level. A high oxygen concentration may becaused by a lean exhaust gas mixture, while a low oxygen concentrationmay be caused by a rich mixture, for example.

The pair of pumping electrodes 212 and 214 is disposed in communicationwith the internal cavity 222, and is configured to electrochemicallypump a selected gas constituent (e.g., O₂) from the internal cavity 222through the layer 201 and out of the sensor 200. Alternatively, the pairof pumping electrodes 212 and 214 may be configured to electrochemicallypump a selected gas through the layer 201 and into the internal cavity222. Herein, the pumping electrodes pair 212 and 214 may be referred toas an O₂ pumping cell.

The electrodes 212, 214, 216, and 218 may be made of various suitablematerials. In some embodiments, the electrodes 212, 214, 216, and 218may be at least partially made of a material that catalyzes thedissociation of molecular oxygen. Examples of such materials include,but are not limited to, electrodes containing platinum and/or gold.

The process of electrochemically pumping the oxygen out of or into theinternal cavity 222 includes applying an electric current I_(p) acrossthe pumping electrodes pair 212 and 214. The pumping current I_(p)applied to the O₂ pumping cell pumps oxygen into or out of the firstinternal cavity 222 in order to maintain a stoichiometric level ofoxygen in the cavity pumping cell. The pumping current I_(p) isproportional to the concentration of oxygen in the exhaust gas. Thus, alean mixture will cause oxygen to be pumped out of the internal cavity222 and a rich mixture will cause oxygen to be pumped into the internalcavity 222.

A control system (not shown in FIG. 2) generates the pumping voltagesignal V_(p) as a function of the intensity of the pumping current I_(p)required to maintain a stoichiometric level within the first internalcavity 222.

As such, the exhaust gas oxygen sensor is operated at a first, lowerreference voltage (Vs), such as 450 mV. However, when the voltage ischanged to a second, higher reference voltage, such as higher than 800mV (e.g., 1080 mV), the sensor dissociates water in the exhaust gas andmeasures the additional oxygen from the water. This phenomenon can thenbe advantageously used to measure ambient humidity. Specifically, whenoperated at the lower reference voltage (450 mV), the pumping current isproportional to the oxygen concentration [O₂]. Then, when the sensor isoperated at the higher reference voltage (1080 mV), additional oxygen isliberated due to the dissociation of water (H₂O->H₂+½O₂) and the changein pumping current corresponding to the excess oxygen is measured todetermine the water concentration [H₂O]. As shown at plot 600 of FIG. 6,the pumping current (Ip, along the y-axis) varies linearly with thewater concentration ([H₂O], along the x-axis). The relationship may bedefined by the equation:

Ip=0.114[H₂O]mA5−0.00011 mA

A linear regression fit of the plot of FIG. 6 provides a regressioncoefficient R² of 0.999. At the higher reference voltage of 1080 mV, thesensor resolution is in the order of 2 μA.

It should be appreciated that the UEGO sensor described herein is merelyan example embodiment of a UEGO sensor, and that other embodiments ofUEGO sensors may have additional and/or alternative features and/ordesigns.

The exhaust gas oxygen sensor, however, is affected by the presence ofhydrocarbons in exhaust air. Specifically, exhaust hydrocarbons may beoxidized to carbon dioxide and water at the sensor, causing the sensingelement of the exhaust gas oxygen sensor to read a lower amount ofoxygen than actually present. As such, this causes ambient humidityestimated based on the output of the UEGO to be incorrect (e.g., theambient humidity is overestimated). While this issue may be somewhataddressed by measuring the amount of water in the air during a DFSOconditions when the engine is not fueled, the measurement maynonetheless be affected by the presence of hydrocarbons ingested fromthe PCV port. These include blow-by gas and positive crankcaseventilation (PCV) hydrocarbons. Even if the PCV port is shut off (e.g.,by closing a PCV valve), PCV hydrocarbons may be ingested through thepiston rings. For example, while an intake throttle is open during theDFSO condition, the intake MAP may be low enough to draw in PCVhydrocarbons. The problem may be exacerbated in aging engines whereadditional PCV leakage may be due to degradation of piston rings andvalves. The increased PCV increases engine oil consumption, loss of peaktorque, and affects the output of the humidity sensor. As such, tocontrol the PCV flow and to identify any major deterioration in enginecomponents, it is required to monitor the PCV flow. However, there is norobust mechanism currently available to determine the PCV flow and/ordetermine the PCV content.

As elaborated with reference to FIGS. 3-5, the inventors herein haverecognized that the impact of the PCV hydrocarbons can be minimized, oreven eliminated, by opening the intake throttle during DFSO events whilethe humidity is being estimated by the exhaust gas oxygen sensor. Byopening the intake throttle, the manifold pressure can be increased.This reduces the delta pressure across the PCV port, thereby reducingthe amount of PCV flow drawn into the intake manifold. The increased MAPalso increases the pressure in the cylinder, reducing the hydrocarbon(or oil) flow across the piston rings into the cylinder air. Further,the increased MAP increases the airflow during the DFSO event, reducingthe oil or hydrocarbon vapor concentration. The combined effect reducesthe overall impact of PCV flow on the exhaust gas sensor's measurementof oxygen from the dissociated ambient humidity water.

In addition, while estimating the ambient humidity, the same exhaust gassensor can be advantageously used to estimate the PCV flow of the engineand identify engine component degradation leading to PCV flow leakage.Specifically, the reference voltage of the exhaust gas oxygen sensor maybe modulated during DFSO events with the intake valve open and then withthe intake valve closed, and the delta Ip at both conditions may becompared to estimate the PCV flow amount. Engine operating parametersmay then be adjusted based on the more accurate estimate of ambienthumidity and PCV flow.

FIGS. 3-5 show flow charts illustrating routines for an exhaust gassensor and an engine system, respectively. For example, the routineshown in FIG. 3 determines whether the sensor should be operated tomeasure exhaust gas oxygen concentration or ambient humidity or PCV flowbased on fueling conditions of the engine. The routine shown in FIG. 4determines the ambient humidity and PCV flow amount based on the exhaustgas sensor 200 described with reference to FIG. 2. FIG. 5 shows aroutine for adjusting an engine operating parameter based on the ambienthumidity and PCV flow determined via the routine shown in FIG. 3. Inaddition, the routine of FIG. 5 allows engine component degradation tobe identified based on PCV flow amount relative to a threshold.

Now turning to FIG. 3, a flow chart illustrating a routine 300 is shownfor controlling an exhaust gas sensor, such as the exhaust gas oxygensensor described above with reference to FIG. 2 and positioned as shownin FIG. 1. The mode of operation of the sensor is controlled based atleast on engine fueling conditions. Specifically, the routine determinesif the engine system is operating under non-fueling conditions andadjusts a measurement mode of the sensor accordingly. For example,during non-fueling conditions, the sensor is operated in a mode todetermine ambient humidity and/or PCV flow while during fuelingconditions, the sensor is operated in a mode to measure exhaust gasoxygen concentration to determine air fuel ratio.

At 302 of routine 300 in FIG. 3, engine operating conditions aredetermined. As non-limiting examples, the engine operating conditionsmay include actual/desired amount of EGR, spark timing, air-fuel ratio,engine speed, barometric pressure, engine coolant temperature, etc.

Once the operating conditions are determined, it is determined if theengine is under non-fueling conditions at 304 of routine 300.Non-fueling conditions include engine operating conditions in which thefuel supply is interrupted but the engine continues spinning and atleast one intake valve and one exhaust valve are operating; thus, air isflowing through one or more of the cylinders, but fuel is not injectedin the cylinders. Under non-fueling conditions, combustion is notcarried out and ambient air may move through the cylinder from theintake passage to the exhaust passage. In this way, a sensor, such as anexhaust gas oxygen sensor, may receive ambient air on whichmeasurements, such as ambient humidity detection, may be performed.

Non-fueling conditions may include, for example, deceleration fuel shutoff (DFSO). DFSO is responsive to the operator pedal (e.g., in responseto a driver tip-out and where the vehicle accelerates greater than athreshold amount). DAFOE conditions may occur repeatedly during a drivecycle, and, thus, numerous indications of the ambient humidity may begenerated throughout the drive cycle, such as during each DFSO event. Assuch, the overall efficiency of the engine may be maintained duringdriving cycles in which the ambient humidity fluctuates. The ambienthumidity may fluctuate due to a change in altitude or temperature orwhen the vehicle enters/exits fog or rain, for example.

If it is determined that the engine is not operating under non-fuelingconditions, for example, fuel is injected in one or more cylinders ofthe engine, routine 300 moves to 308. At 308, the exhaust gas sensor isoperated as an air-fuel ratio sensor. In this mode of operation, thesensor may be operated as a lambda sensor, for example. As a lambdasensor, the output voltage may determine whether the exhaust gasair-fuel ratio is lean or rich. Alternatively, the sensor may operate asa universal exhaust gas oxygen sensor (UEGO) and an air-fuel ratio(e.g., a degree of deviation from a stoichiometric ratio) may beobtained from the pumping current of the pumping cell of the sensor.

At 310 of routine 300, the air-fuel ratio (FAR) is controlled responsiveto the exhaust gas oxygen sensor. Thus, a desired exhaust gas FAR may bemaintained based on feedback from the sensor during engine fuelingconditions. For example, if a desired air-fuel ratio is thestoichiometric ratio and the sensor determines the exhaust gas is lean(i.e., the exhaust gas comprises excess oxygen and the FAR is less thanstoichiometric), additional fuel may be injected during subsequentengine fueling operation. As another example, if a desired air-fuelratio is the stoichiometric ratio and the sensor determines the exhaustgas is rich (i.e., the exhaust gas comprises excess fuel and the FAR ismore than stoichiometric), fuel injection may be reduced duringsubsequent engine fueling operation.

On the other hand, if it is determined that the engine is undernon-fueling conditions, the routine proceeds to 306, and the sensor isoperated to determine ambient humidity and/or PCV flow to the engine.The ambient humidity and the PCV flow may be determined based on thesensor output, as described in greater detail below with reference toFIG. 4. For example, a reference voltage of the sensor may be modulatedbetween a minimum voltage at which oxygen is detected and a voltage atwhich water molecules may be dissociated such that the ambient humiditymay be determined. The process may be repeated with the intake throttleopen (where PCV flow is reduced or eliminated) as well as the intakethrottle closed (where PCV flow is enabled) and the difference in sensoroutputs at the two throttle conditions may be used to infer PCV flow. Itshould be understood, the ambient humidity as determined (describedbelow with reference to FIG. 4) is the absolute ambient humidity.Additionally, relative humidity may be obtained by further employing atemperature detecting device, such as a temperature sensor.

FIG. 4 shows a flow chart illustrating a routine 400 for determiningambient humidity and PCV flow via an exhaust gas sensor, such as theoxygen sensor described above with reference to FIG. 2, and positionedas shown in FIG. 1, for example.

At 401, the routine includes closing a PCV port. For example, if a PCVvalve coupling the engine crankcase to the intake manifold is present,the valve may be closed. By closing the valve, ingestion of PCVhydrocarbons is reduced, and their effect on the output of the exhaustgas oxygen sensor is minimized.

At 402, the routine includes opening an intake throttle to increase themanifold pressure (MAP) and thereby reduce the drawing in of PCV flowpast piston rings. Opening the intake throttle includes fully openingthe intake throttle in one example. In another example, the intakethrottle may be opened by at least 15 degrees. As discussed previously,by opening the intake throttle, the impact of PCV flow (such as any PCVflow leaking past the piston rings) is reduced. This is due to theincrease in MAP causing a drop in delta pressure across the PCV port,which reduces the amount of PCV flow into the intake manifold. Theincreased MAP also increases the cylinder pressure which reduces theflow of PCV hydrocarbons across the piston rings into the cylinder air.Finally, the increased MAP also increases the overall airflow during theDFSO event, reducing the effective hydrocarbon vapor concentration.

At 404, the routine includes, with the intake throttle open, modulatinga reference voltage of the exhaust gas sensor. Herein, the exhaust gassensor is an exhaust gas oxygen sensor. Modulating the reference voltageincludes switching the reference voltage between a first, lowerreference voltage and a second, higher reference voltage. Specifically,at 406, the sensor is operated at the lower reference voltage and afirst pumping current output by the sensor (IP1) is read. Then, at 408,the reference voltage is increased, the sensor is operated at the higherreference voltage, and a second pumping current output by the sensor(IP2) is read. As one non-limiting example, the first voltage may be 450mV and the second voltage may be 1080 mV. With the intake throttle open,at 450 mV, for example, the first pumping current (IP1=Ip_(—)450_no_pcv)may be indicative of an amount of oxygen in the exhaust gas. At 1080 mV,water molecules may be dissociated such that the second pumping currentis indicative of the amount of oxygen in the exhaust gas plus an amountof oxygen from dissociated water molecules (IP2=Ip_(—)1080_no_pcv). Thefirst voltage may be a voltage at which a concentration of oxygen in theexhaust gas may be determined, for example, while the second voltage maybe a voltage at which water molecules may be dissociated.

As such, at 1080 mV, carbon dioxide (CO₂) molecules may be dissociatedin addition to water molecules. However, during conditions when theintake throttle is open, and the engine is not fueled, carbon dioxidefrom hydrocarbon (e.g., fuel or oil) oxidation may not be generated andtherefore may not affect the humidity estimation.

At 408, the routine includes determining a change in pumping current(delta Ip) during the modulation. At 410, an average change in pumpingcurrent may be determined. For example, during the DFSO event with theintake throttle open, the modulating may be performed for a duration,and a change in pumping current at each modulation may be learned. Then,the learned values may be averaged. As such, since this delta Ip isbased on sensor output read with the intake throttle open, the delta Iprepresents the change in pumping current from ambient humidity only(without any contribution from PCV flow). Thus, this first change inpumping current may be stored as Delta_ip_no_pcv and may be learned as:

Delta_(—) ip_no_pcv=Ip _(—)1080_no_pcv−Ip _(—)450_no_pcv=IP2−IP1

By modulating the reference voltage and determining an average change inpumping current, the effect of a changing air fuel ratio at thebeginning of a fuel shut off duration when residual combustion gases maybe present in the exhaust may be nullified, for example. As such, anindication of ambient humidity may be generated relatively quickly afterfuel injection is suspended, even if the exhaust gas is not free ofresidual combustion gases.

At 412, an ambient humidity may be estimated based on the first changein pumping current (Delta_ip_no_pcv). Specifically, since the pumpingcurrent output by the sensor at the second voltage (where watermolecules are dissociated) is indicative of the amount of oxygen in theexhaust gas plus an amount of oxygen from dissociated water molecule,while the first pumping current output by the sensor at the firstvoltage (where water molecules are not dissociated) is indicative of theamount of oxygen in the exhaust gas, the first change in pumping current(difference between first pumping current and second pumping currentwith intake throttle open) estimated during the engine non-fuelingcondition where at least one intake valve and one exhaust valve isoperating is indicative of the ambient humidity.

It will be appreciated that in some examples, modulating of thereference voltage for determination of ambient humidity may be based onthe duration of the fuel shut off. For example, the routine mayoptionally determine a duration since fuel shut off. If the durationsince fuel shut off is less than a threshold duration, the referencevoltage of the sensor is modulated between the first voltage and thesecond voltage in order to determine the ambient humidity. When theduration since fuel shut off is greater than the threshold duration, thereference voltage is not modulated. In some examples, the duration sincefuel shut off may be a time since fuel shut off. In other examples, theduration since fuel shut off may be a number of engine cycles since fuelshut off. As such, the threshold duration may be an amount of time untilthe exhaust is substantially free of hydrocarbons from combustion in theengine. For example, residual gases from one or more previous combustioncycles may remain in the exhaust for several cycles after fuel is shutoff and the gas that is exhausted from the chamber may contain more thanambient air for a duration after fuel injection is stopped. Further, theperiod in which fuel is shut off may vary. For example, a vehicleoperator may release the accelerator pedal and coast to a stop,resulting in a long DFSO period. In some situations, the fuel shut offperiod (the time from interruption of the fuel supply to restart of thefuel supply, for example) may not be long enough for the ambient air toestablish an equilibrium state in the exhaust system. For example, avehicle operator may tip-in shortly after releasing the acceleratorpedal, causing DFSO to stop soon after beginning. In such a situation,the controller may modulate the reference voltage, as discussed at 404.In comparison, if the duration since fuel shut off is greater than thethreshold duration, the reference voltage is increased to a thresholdvoltage, but not modulated. The threshold voltage may be a voltage atwhich a desired molecule is dissociated, such as the second, higherreference voltage of 1080 mV. In another example, during humidityestimation only (not PCV flow estimation), the second, higher referencevoltage used may be 950 mV or another voltage at which water moleculesmay be dissociated.

Returning to routine 400, after estimating the ambient humidity, at 414,the routine includes closing the intake throttle to decrease themanifold pressure (MAP) and thereby raise the drawing in of PCV flowpast piston rings into the engine intake manifold. Closing the intakethrottle includes fully closing the intake throttle. As such, by closingthe intake throttle, the impact of PCV flow is increased.

Next, at 416, with the intake throttle closed, the reference voltage ofthe exhaust gas oxygen sensor is modulated. As discussed with referenceto 404, modulating the reference voltage includes switching thereference voltage between the first, lower reference voltage (e.g., 450mV) and the second, higher reference voltage (e.g., 1080 mV).Specifically, at 418, the sensor is operated at the lower referencevoltage and a first pumping current output by the sensor(IP1′=Ip_(—)450_w_pcv) is read. Then, at 419, the reference voltage isincreased, the sensor is operated at the higher reference voltage, and asecond pumping current output by the sensor (IP2′=Ip_(—)1080_w_pcv) isread. With the intake throttle closed, at 450 mV, for example, thepumping current may be indicative of an amount of oxygen in the exhaustgas. With the throttle closed, at 1080 mV, carbon dioxide (CO₂)molecules may be dissociated in addition to water molecules.Specifically, during conditions when the intake throttle is closed, andthe engine is not fueled, carbon dioxide from hydrocarbon (e.g., fuel oroil) oxidation may be generated and may therefore affect the humidityestimation. Thus, at 1080 mV, water molecules and carbon dioxidemolecules may be dissociated such that the pumping current is indicativeof the amount of oxygen in the exhaust gas plus an amount of oxygen fromdissociated water molecules plus an amount of oxygen from dissociatedcarbon dioxide (CO₂) molecules. The CO₂ is generated from the PCVhydrocarbons reacting with oxygen at the sensing element of the exhaustgas oxygen sensor to generate CO₂ and water.

At 420, the routine includes determining a change in pumping current(delta Ip) during the modulation. At 422, an average change in pumpingcurrent may be determined. For example, during the DFSO event with theintake throttle closed, the modulating may be performed for a duration,and a change in pumping current at each modulation may be learned. Then,the learned values may be averaged. As such, since this delta Ip isbased on sensor output read with the intake throttle closed, the deltaIp represents the change in pumping current from ambient humidity withadditional contribution from PCV flow. Thus, this second change inpumping current may be stored as Delta_ip_w_pcv and learned as:

Delta_(—) ip _(—) w_pcv=Ip _(—)1080_(—) w_pcv−Ip _(—)450_(—)w_pcv=IP2′−IP1′

At 424, PCV flow may be estimated based on outputs of the exhaust gasoxygen sensor during the modulating with the intake throttle open andclosed. Specifically, PCV flow rate (at closed throttle conditions) isestimated based on (e.g., as a function of) a difference between thefirst change in pumping current output by the sensor during themodulating with the intake throttle open (Delta_ip_no_pcv, as determinedat 408) and the second change in pumping current output by the sensorduring the modulating with the intake throttle closed (Delta_ip_w_pcv,as determined at 422). In other words, PCV flow may be determined as perthe equation:

PCV_flow=f(Delta_(—) ip _(—) w_pcv−Delta_(—) ip_no_pcv) whereinf=function of

As elaborated with reference to FIG. 5, an engine controller may thenindicate engine degradation (e.g., engine component degradation) basedon the estimated PCV flow. Further, the controller may adjust an engineoperating parameter based on the indication of ambient humidity (aslearned at 412) and the estimated PCV flow (as learned at 424).

It will be appreciated that in some embodiments, the indication ofambient humidity may be generated based on the output of the sensor withthe intake throttle open and further based on the estimated PCV flow.

In this way, the controller may first modulate the reference voltage ofthe exhaust gas sensor between the first, lower voltage and the second,higher voltage with the intake throttle open, and then close the intakethrottle and modulate the reference voltage again between the first andsecond voltages with the intake throttle closed. The controller may thenestimate an ambient humidity based on the outputs of the sensor duringthe modulating with the intake throttle open while estimating the PCVflow based on the outputs of the sensor during the modulating with theintake throttle open relative to the outputs of the sensor during themodulating with the intake throttle closed.

As described in detail above, an exhaust gas sensor may be operated invarious modes in which the pumping voltage or pumping current of thepumping cell is monitored. As such, the sensor may be employed todetermine the absolute ambient humidity of the air surrounding thevehicle, the PCV flow through the engine, as well as the air-fuel ratioof the exhaust gas. Subsequent to detection of the ambient humidity, thePCV flow, and the air-fuel ratio, a plurality of engine operatingparameters may be adjusted for optimal engine performance, which will beexplained in detail below. These parameters include, but are not limitedto, an amount of exhaust gas recirculation (EGR), spark timing, air-fuelratio, fuel injection, and valve timing. In one embodiment, one or moreof these operating parameters (e.g., EGR, spark timing, air-fuel ratio,fuel injection, valve timing, etc.) are not adjusted during themodulating of the reference voltage of the exhaust gas sensor.

FIG. 5 shows a flow chart illustrating a routine 500 for adjustingengine operating parameters based on an ambient humidity generated by anexhaust gas sensor, such as the ambient humidity generated as describedwith reference to FIG. 4, for example. The engine operating parametersmay be further adjusted based on the estimated PCV flow. For example, anincrease in water concentration of the air surrounding the vehicle maydilute a charge mixture delivered to a combustion chamber of the engine.If one or more operating parameters are not adjusted in response to theincrease in humidity, engine performance and fuel economy may decreaseand emissions may increase; thus, the overall efficiency of the enginemay be reduced. As another example, the presence of PCV flow into theengine may increase the fuel content of the air entering the cylinders.If cylinder fuel injection is not adjusted in response to the increasein fuel, engine performance and fuel economy may decrease and emissionsmay increase; thus, the overall efficiency of the engine may be reduced.

At 502, engine operating conditions are determined. The engine operatingconditions may include EGR, spark timing, and air fuel ratio, amongothers, which may be affected by fluctuations of the water concentrationin ambient air.

Once the operating conditions are determined, the routine proceeds to504 where the ambient humidity estimated learned during the routine ofFIG. 4 is retrieved. Once the ambient humidity is retrieved, the routinecontinues to 506 where the PCV flow amount learned during the routine ofFIG. 4 is retrieved. At 508, upon retrieving both the PCV flow and theambient humidity estimate, one or more operating parameters are adjustedbased on the estimated ambient humidity and the PCV flow. Such operatingparameters may include an amount of EGR, spark timing, and air-fuelratio, among others. As described above, in internal combustion engines,it is desirable to schedule engine operating parameters, such as sparktiming, in order to optimize engine performance. In addition, enginecontrol functions that are impacted by ambient humidity are adjusted.These may include, for example, spark compensation (e.g., sparkcompensation factors), condensation models (e.g., condensation modelingcoefficients), as well as humidity sensor diagnostics (e.g., thresholdsfor humidity sensor OBD routines). Engine operating parameters affectedby PCV flow may include, for example, fuel injection amounts. In someembodiments, only one parameter may be adjusted responsive to thehumidity and PCV flow. In other embodiments, any combination orsub-combination of these operating parameters may be adjusted inresponse to measured fluctuations in ambient humidity.

In one example embodiment, an amount of EGR may be adjusted based on themeasured ambient humidity. For example, in one condition, the waterconcentration in the air surrounding the vehicle may have increased dueto a weather condition such as fog; thus, a higher humidity is detectedby the exhaust gas sensor during engine non-fueling conditions. Inresponse to the increased humidity measurement, during subsequent enginefueling operation, the EGR flow into at least one combustion chamber maybe reduced. As a result, engine efficiency may be maintained.

Responsive to a fluctuation in absolute ambient humidity, EGR flow maybe increased or decreased in at least one combustion chamber. As such,the EGR flow may be increased or decreased in only one combustionchamber, in some combustion chambers, or in all combustion chambers.Furthermore, the magnitude of change of the EGR flow may be the same forall cylinders or the magnitude of change of the EGR flow may vary bycylinder based on the specific operating conditions of each cylinder.

In another embodiment, spark timing may be adjusted responsive to theambient humidity. In at least one condition, for example, spark timingmay be advanced in one or more cylinders during subsequent enginefueling operation responsive to a higher humidity reading. Spark timingmay be scheduled so as to reduce knock in low humidity conditions (e.g.,retarded from a peak torque timing), for example. When an increase inhumidity is detected by the exhaust gas sensor, spark timing may beadvanced in order to maintain engine performance and operate closer toor at a peak torque spark timing.

Additionally, spark timing may be retarded in response to a decrease inambient humidity. For example, a decrease in ambient humidity from ahigher humidity may cause knock. If the decrease in humidity is detectedby the exhaust gas sensor during non-fueling conditions, such as DFSO,spark timing may be retarded during subsequent engine fueling operationand knock may be reduced.

It should be noted that spark may be advanced or retarded in one or morecylinders during subsequent engine fueling operation. Further, themagnitude of change of spark timing may be the same for all cylinders orone or more cylinders may have varying magnitudes of spark advance orretard.

In still another example embodiment, exhaust gas air fuel ratio may beadjusted responsive to the measured ambient humidity during subsequentengine fueling operation. For example, an engine may be operating with alean air fuel ratio optimized for low humidity. In the event of anincrease in humidity, the mixture may become diluted, resulting inengine misfire. If the increase in humidity is detected by the exhaustgas sensor during non-fueling conditions, however, the air fuel rationmay be adjusted so that the engine will operate with a less lean, leanair fuel ratio during subsequent fueling operation. Likewise, an airfuel ratio may be adjusted to be a more lean, lean air fuel ratio duringsubsequent engine fueling operation in response to a measured decreasein ambient humidity. In this way, conditions such as engine misfire dueto humidity fluctuations may be reduced.

In some examples, an engine may be operating with a stoichiometric airfuel ratio or a rich air fuel ratio. As such, the air fuel ratio may beindependent of ambient humidity and measured fluctuations in humiditymay not result in an adjustment of air fuel ratio.

In yet another embodiment, fuel injection may be adjusted responsive tothe PCV flow with the fuel injection during subsequent engine fuelingconditions (that is, engine fueling conditions following the DFSO eventwhere the humidity and PCV flow was learned) decreased as the PCV flowis increased.

From 506, the routine may also move to 510-512 to identify enginecomponent degradation based on the estimated PCV flow. Specifically, at510, the estimated PCV flow may be compared to a threshold. Thethreshold may be based on PCV flow levels measured during known enginedegradation. Alternatively, the threshold may be based on a change inair-fuel ratio modeled based on the PCV flow. At 512, the routineincludes indicating engine degradation based on the estimated PCV flowbeing higher than the threshold. Indicating engine degradation mayinclude indicating degradation of engine components such as piston ringsor valves. As such, if the estimated PCV flow is not higher than thethreshold, no degradation may be determined and the routine may end.

In some embodiments, in response to the indication of degradation, adiagnostic code may be set. One or more engine operating parameters mayoptionally be further adjusted based on the indication. For example, anamount of EGR may be reduced based on the estimated PCV flow beinghigher than the threshold.

In one example, an engine method includes, during a first enginenon-fueling condition, opening an intake throttle, modulating areference voltage of an exhaust gas oxygen sensor, and learning a firstchange in sensor output during the modulating. Then, during a secondengine non-fueling condition, the method includes closing the intakethrottle, modulating the reference voltage of the exhaust gas oxygensensor, and learning a second change in sensor output during themodulating. The method then generates an indication of PCV flow based onthe first change relative to the second change. Herein, the first changein sensor output is a first change in pumping current output by thesensor during the modulating with the intake throttle open, while thesecond change in sensor output is a second change in pumping currentoutput by the sensor during the modulating with the intake throttleclosed. The method further includes generating an indication of ambienthumidity based on the first change but not the second change in sensoroutput.

Further, the first change may be a first average change whereingenerating an indication of ambient humidity based on the first changeduring the first non-fueling condition includes generating a change inpumping current for each modulation, averaging the change in pumpingcurrent, and generating an indication of ambient humidity based on theaverage of the change in pumping current.

The method further includes, during an engine fueling conditionfollowing the first and second engine non-fueling conditions, adjustingan engine operating parameter based on each of the indication of ambienthumidity and the indication of PCV flow, the engine operating parameterincluding one or more of an amount of exhaust gas recirculation, sparktiming, fuel injection amount, and engine air fuel ratio. As such,during each of the first and second engine non-fueling conditions, aport coupling an engine crankcase to the intake manifold is closed.Furthermore, piston valve degradation is indicated in response to theindication of PCV flow being higher than a threshold.

Now turning to FIG. 7, the impact of PCV flow on humidity determinationis shown. In particular, map 700 shows an example change in pumpingcurrent of an exhaust gas oxygen sensor at different reference voltages.Map 700 depicts DFSO conditions at plot 702, a reference voltage appliedto the sensor at plot 704, a pumping current output without PCV flow atplot 706 relative to the pumping current output with PCV flow at plot708.

From t0 to t5, an engine DFSO event may occur (plot 702). In response tothe DFSO event at t0, the reference voltage (Vref) applied to an exhaustgas oxygen sensor may be modulated between a higher voltage (such as1080 mV) and a lower voltage (such as 450 mV), as shown at plot 704. Apumping current (Ip) output by the sensor in response to the applicationof the reference voltage may be observed. Plot 706 (darker line) showsthe change in pumping current of the exhaust gas oxygen sensorresponsive to the modulation of the reference voltage in the absence ofany PCV flow, such as when the modulation is performed with the intakethrottle open. As shown at 710, in the absence of PCV flow, a smallerchange in pumping current (delta Ip 710) is noted wherein delta Ip 710corresponds to an intake oxygen concentration due to dissociated watermolecules. Therefore, an ambient humidity can be inferred from delta Ip710 during the DFSO condition.

Plot 708 (lighter line) shows the change in pumping current of theexhaust gas oxygen sensor responsive to the modulation of the referencevoltage in the presence of PCV flow, such as when the modulation isperformed with the intake throttle closed. As shown at 712, in thepresence of PCV flow, a larger change in pumping current (delta Ip 712)is noted wherein delta Ip 712 corresponds to an intake oxygenconcentration due to dissociated water molecules as well as dissociatedCO2 molecules from the oxidation of PCV hydrocarbons at the exhaustoxygen sensor. As can be seen, the presence of PCV flow has a largeimpact on the output of the sensor, and therefore any humidityestimation performed in the presence of PCV flow, based on delta Ip 712,may incorrectly estimate a higher ambient humidity than an actualambient humidity. As explained at FIG. 4, delta Ip 712 can be used tolearn the PCV flow rate. Specifically, by comparing delta Ip 712 withdelta Ip 710, the impact of PCV flow can be learned and the PCV flow canbe inferred. Specifically, PCV flow rate can be learned as a function ofthe difference between delta Ip 712 and delta Ip 710 during the selectedDFSO conditions.

At t5, the DFSO condition may end, cylinder fueling may resume, and theoutput of the sensor may not be used for humidity estimation. As such,during fueling conditions, the output of the exhaust gas oxygen sensorcan be used for estimating an exhaust air-fuel ratio (as discussed atFIG. 3) as well as the ethanol content of fuel burned in the engine.

In one example, an engine system comprises an engine with an intake andan exhaust manifold, an exhaust gas oxygen sensor disposed in theexhaust manifold upstream of an exhaust catalyst, an intake throttledisposed in the exhaust manifold, a PCV port configured to deliverblow-by gases from a crankcase of the engine to the intake manifold; anda control system in communication with the sensor. The control systemincludes non-transitory instructions to: during an engine decelerationfuel shut off (DFSO), close the PCV port; fully open the intakethrottle; modulate a reference voltage of the sensor between a first,lower voltage and a second, higher voltage; and generate an indicationof ambient humidity based on a first change in pumping currentresponsive to the modulating of the reference voltage. The controllerincludes further instructions for, maintaining the PCV port closed;fully closing the intake throttle; re-modulating the reference voltageof the sensor; and generating an indication of PCV flow into the intakemanifold based on a second change in pumping current responsive to there-modulating of the reference voltage relative to the first change inpumping current. Then, during an engine fueling condition following theengine DFSO, the controller may adjust one or more of exhaust gasrecirculation, engine air fuel ratio, and spark timing based on theambient humidity.

In this way, an ambient humidity estimate can be accurately generated byan exhaust gas oxygen sensor during DFSO conditions with minimal impacton the humidity estimate from PCV flow. By closing the throttle duringthe DFSO conditions when humidity is estimated, PCV flow the engine isreduced, and the hydrocarbon effect of the PCV flow on the sensor outputis reduced. During the same DFSO conditions, by modulating the referencevoltage of the sensor both with the intake throttle open and with theintake throttle closed, the change in pumping current at the sensor canbe advantageously used to learn the PCV flow to the engine. This notonly allows PCV flow to be measured, but also enabled earlyidentification of engine component degradation and engine aging leadingto leakage of PCV hydrocarbons. One or more engine operating parametersmay be then adjusted responsive to the ambient humidity estimate and thePCV flow estimate. As DFSO may occur numerous times during a drivecycle, an ambient humidity measurement may be generated several timesthroughout the drive cycle and one or more engine operating parametersmay be adjusted accordingly, resulting in an optimized overall engineperformance despite fluctuations in ambient humidity. Furthermore, theengine operating parameters may be adjusted responsive to the ambienthumidity regardless of a duration the engine non-fueling conditions, asan indication of ambient humidity may be generated in a short amount oftime even if the exhaust gas is not devoid of residual combustion gasesby modulating the reference voltage.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory. The specific routinesdescribed herein may represent one or more of any number of processingstrategies such as event-driven, interrupt-driven, multi-tasking,multi-threading, and the like. As such, various actions, operations,and/or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedactions, operations and/or functions may be repeatedly performeddepending on the particular strategy being used. Further, the describedactions, operations and/or functions may graphically represent code tobe programmed into non-transitory memory of the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method for an engine system, comprising: during engine non-fuelingconditions, where at least one intake valve and one exhaust valve areoperating: modulating a reference voltage of an exhaust gas sensor withan intake throttle closed and open; and indicating engine degradationbased on positive crankcase ventilation (PCV) flow, the PCV flow basedon outputs of the sensor during the modulating.
 2. The method of claim1, wherein opening the intake throttle includes fully opening the intakethrottle.
 3. The method of claim 1, wherein the exhaust gas sensor is anexhaust gas oxygen sensor.
 4. The method of claim 1, wherein modulatingthe reference voltage includes switching the reference voltage between afirst, lower voltage and a second, higher voltage.
 5. The method ofclaim 1, wherein indicating engine degradation based the estimated PCVflow includes indicating engine degradation based on the estimated PCVflow being higher than a threshold.
 6. The method of claim 5, whereinmodulating the reference voltage of the exhaust gas sensor with theintake throttle closed and open includes first modulating the referencevoltage between the first and second voltage with the intake throttleopen, then closing the intake throttle, and then modulating thereference voltage between the first and second voltage with the intakethrottle closed.
 7. The method of claim 6, wherein estimating PCV flowbased on outputs of the sensor during the modulating includes estimatingPCV flow based on a difference between a first change in pumping currentoutput by the sensor during the modulating with the intake throttle openand a second change in pumping current output by the sensor during themodulating with the intake throttle closed.
 8. The method of claim 7,further comprising, generating an indication of ambient humidity basedon an output of the exhaust gas sensor with the intake throttle open. 9.The method of claim 8, further comprising, adjusting an engine operatingparameter based on the indication of ambient humidity and the estimatedPCV flow.
 10. The method of claim 9, wherein the engine operatingparameter includes an amount of exhaust gas recirculation, and whereinthe adjusting an amount of exhaust gas recirculation includes reducingthe amount of exhaust gas recirculation responsive to one or more of anindication of higher ambient humidity and an indication of higher thanthreshold PCV flow.
 11. The method of claim 1, wherein the enginenon-fueling conditions include a deceleration fuel shut off (DFSO). 12.A method for an engine, comprising: during a first engine non-fuelingcondition, opening an intake throttle, modulating a reference voltage ofan exhaust gas oxygen sensor, and learning a first change in sensoroutput during the modulating; during a second engine non-fuelingcondition, closing the intake throttle, modulating the reference voltageof the exhaust gas oxygen sensor, and learning a second change in sensoroutput during the modulating; and generating an indication of PCV flowbased on the first change relative to the second change.
 13. The methodof claim 12, wherein the first change in sensor output is a first changein pumping current output by the sensor during the modulating with theintake throttle open, and wherein the second change in sensor output isa second change in pumping current output by the sensor during themodulating with the intake throttle closed.
 14. The method of claim 13,further comprising, generating an indication of ambient humidity basedon the first change but not the second change in sensor output.
 15. Themethod of claim 14, wherein the first change is a first average changeand wherein generating an indication of ambient humidity based on thefirst change during the first non-fueling condition, generating a changein pumping current for each modulation; averaging the change in pumpingcurrent; and generating an indication of ambient humidity based on theaverage of the change in pumping current.
 16. The method of claim 15,further comprising, during an engine fueling condition following thefirst and second engine non-fueling conditions, adjusting an engineoperating parameter based on each of the indication of ambient humidityand the indication of PCV flow, the engine operating parameter includingone or more of an amount of exhaust gas recirculation, spark timing,fuel injection amount, and engine air fuel ratio.
 17. The method ofclaim 12, wherein during each of the first and second engine non-fuelingconditions, a port coupling an engine crankcase to the intake manifoldis closed.
 18. The method of claim 17, further comprising, indicatingpiston valve degradation in response to the indication of PCV flow beinghigher than a threshold.
 19. An engine system, comprising: an enginewith an intake and an exhaust manifold; an exhaust gas oxygen sensordisposed in the exhaust manifold upstream of an exhaust catalyst; anintake throttle disposed in the exhaust manifold; a PCV port configuredto deliver blow-by gases from a crankcase of the engine to the intakemanifold; and a control system in communication with the sensor, thecontrol system including non-transitory instructions for: during anengine deceleration fuel shut off (DFSO), closing the PCV port; fullyopening the intake throttle; modulating a reference voltage of thesensor between a first, lower voltage and a second, higher voltage; andgenerating an indication of ambient humidity based on a first change inpumping current responsive to the modulating of the reference voltage.20. The system of claim 18, wherein the controller includes furtherinstructions for, maintaining the PCV port closed; fully closing theintake throttle; re-modulating the reference voltage of the sensor; andgenerating an indication of PCV flow into the intake manifold based on asecond change in pumping current responsive to the re-modulating of thereference voltage relative to the first change in pumping current. anengine fueling condition following the engine DFSO, adjust one or moreof exhaust gas recirculation, engine air fuel ratio, and spark timingbased on the ambient humidity.